Miniaturization in microelectronics will continue to progress rapidly in accordance with the International Technology Roadmap for Semiconductors (ITRS). According to this, in 2010 and 2016, 45 nm and 22 nm lines are respectively expected for DRAMs and values of 25 nm and 13 nm are respectively expected for the geometrical gate lengths of microprocessors (MPU).
For the mass production of structures with a size of 45 nm or less, optical lithography in the soft X-ray range at 13.5 nm, so-called extreme ultraviolet lithography (EUV lithography), is rated as the most promising lithography technology. However, it will only be used when not only the required resolution but also the required linewidth fluctuations are complied with, which are generally less than 10% of the minimum line widths, i.e. in 2010 approximately 4 nin for DRAMs and approximately 2 nm for MPU gate lengths. For 2016, the corresponding values will even be 2 nm and 1 nm, respectively. The edge roughness of the resist structures is therefore permitted to exceed scarcely half of these values per side. Only edge roughnesses of approximately 6 to 10 nm are currently being achieved, however, which is inadequate even for the 50 nm node in 2009.
A series of causes contribute to the edge roughness of resist structures that are produced lithographically. In some instances, work on measures for minimizing the edge roughness is already being carried out very successfully.
Thus, by way of example, high resolution electron beam writing and anisotropic etching processes are being used in attempts to transfer the resist structures to the mask blank as dimensionally faithfully as possible in order to minimize the linewidth fluctuations or the edge roughness on the mask.
Furthermore, the imaging performance of the projection optical system is being optimized, by way of example, in particular increasing the resolution, reduction of wavefront errors, reduction of light scattering (flare), exact function of the scanning tables for mask and wafer and also minimization of aberrations.
Furthermore, use is made of photoresists (resists) which make the least possible contribution to the edge roughness, e.g. by using basic polymers with different types of linear or ring-type molecular elements that are as small as possible, and minimizing the diffusion lengths of the photochemically generated protons, e.g. by the addition of bases.
However, a photoresist is intended to have a high sensitivity for large throughput and a high contrast, but experience shows that this can be achieved only at the expense of higher edge roughness.
As set forth above, ever smaller structures will be required in the future in order to further improve microelectronics. Since, in the case of ever smaller structures, low edge roughness of these structures is of enormous importance, there is a perceived need for a method for producing structures with the least possible edge roughness.